Process for carbonizing cellulosic textile materials



United States Patent 3,333,926 PROCESS FOR CARBONIZING CELLULOSIC TEXTILE MATERIALS Ralph 0. Moyer, Jr., Donald R. Ecker, and William J. Spry, Jr., Fostoria, Ohio, assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Oct; 30, 1963, Ser. No. 319,939 9 Claims. (Cl. 23-209.1)

ABSTRACT OF THE DISCLOSURE C. to produce a carbon textile. If desired, the resultant carbon textile can be converted to a graphite textile by subsequently heating it to graphitizing temperatures in an oxygen-free, non-carbonaceous gaseous atmosphere containing at least about of a halogen gas.

This invention relates to a process for manufacturing from cellulosic textile starting materials, carbonaceous materials which possess textile characteristics, and has for its object the provision of a process which yields flexible carbonaceous materials having improved strength characteristics.

The term carbonaceous is intended to encompass both carbon and graphite. The term flexible carbonaceous fibers refers to materials which have the physical properties of a textile, such as hand and drape, coupled with the attendant chemical and electrical properties of carbon and graphite.

Carbonaceous filaments and processes for producing the same are known to the prior art. Such filamentary materials are the result of work ranging from the early work of Thomas A. Edison and W. R. Whitney, whose filaments were rather inflexible and did not retain the textile characteristics of the starting material, to the recently manufactured carbonaceous materials exemplified by Soltes, US. Patent 3,011,981 and Abbott, U.S. Patent 3,053,775 whose materials are reported to possess the typical attendant unique electrical, chemical and mechanical properties of natural carbonaceous material in the form of textile structures such as yarn and cloth which also retain the textile properties, such as drape and hand, of the starting materials. In addition, electrically conductive graphite in a flexible fiber and fabric form is reported in Metals Progress, May 1959, pp. 115-116, and is commercially available in any textile form such as yarn, braid, felt and woven cloth and knit fabrics.

Improved processes for the production of carbon and graphite textile materials are also disclosed in United States Patents 3,107,152 and 3,116,975, both of which are assigned to a common assignee with the subject application.

All of the above dis-cussed processes and products thereof have in common the slow and gradual carbonization of a cellulosic starting material by selected pyrolysis processes. The cellulosic starting materials which have been 3,333,926 Patented Aug. 1, 1967 employed have been both natural cellulose such as cotton and regenerated cellulose such as rayon. Once the cellulosic material has been carbonized by heating to temperatures of the order of 800 C., the material may be graphitized by further heating at any desired rate which is convenient.

In the aforementioned Patent No. 3,116,975, it is disclosed that a critical stage of processing is encountered when gases evolve from the cellulosic material being processed, particularly during the graphitization stage. It is stated therein that in order to ensure the production of clean, flexible, graphite textile material, any such gases which evolve from the material must be controlled in order to prevent an undesirable graphite soot from being deposited on the material being processed. This soot was attributed to low molecular weight hydrocarbons, such as methane, which are evolved from cellulose at elevated temperatures. These gases redeposit on the fibers as a graphite soot as a result of thermal cracking at higher temperatures. This soot will also cause individual filaments to stick to one another, particularly on cross sections of the material and thereby the production of a weak brittle product is encouraged.

The above discussed problem is avoided according to Patent No. 3,116,975 by .graphitizing the cellulosic starting material, which had previously been carbonized at temperatures of about 800 C. in an electric furnace at temperatures of about 2500 C. while continuously purging the furnace with an oxygen free, non-carbonaceous gas, specifically nitrogen, argon or helium gas, until substantially complete graphitization of the material has occurred. The purging is suitably carried out by impinging large volumes of the gas against the surface of the material being graphitized, thereby sweeping the surface of the material free from any soot which may attempt to deposit on the surface thereof.

It has been unexpectedly discovered, and this discovery forms the basis of the subject invention, that if a halogen gas containing oxygen free, non-carbonaceous gaseous atmosphere is employed during the graphitization stage rather than a nitrogen, argon or helium atmosphere, 2. much higher strength product is realized. Of the halogen gases, chlorine is preferred and for sirnplicitys sake the ensuing discussion will be specifically directed to chlorine, but this is not intended to exclude the other halogens from the scope of the invention.

More specifically, in the practice of the invention, the

nitrogen atmosphere which is normally employed in a purging manner during graphitization of the already carbonized cellulosic starting material is either partially or totally replaced with-an atmosphere of chlorine gas. While an atmosphere of 100% chlorine gas is effective in realizing the higher strength product, a mixture of as low as 5% chlorine with an oxygen-free, non-carbonaceous gas is suitable, and the preferred atmosphere comprises approximately 20% chlorine and nitrogen.

In the table, below, the properties for graphite cloth produced by heating pre-carbonized cellulosic cloth in an electrically heated graphite tube furnace in a nitrogen atmosphere, the nitrogen being fed in both ends of the furnace, sweeping the surface of the cloth being graphitized and venting from the center of the furnace at all times the temperature is above about 800 C., are compared with the properties of graphite cloth similarly produced in an atmosphere comprising 20% chlorine and 80% nitrogen.

TABLE Control N o. Samples Avg.* Min Max samples I Avg.* MID Max Width, in 26 43. 9 42. 5 44. 5 2 We ght, oz /sq. yard 2G 7. 64 7.17 8.15 2 Thickness, in 20 0. 0249 0.0236 0. 0276 2 Count, threads/in tarp 26 26. 92 24.0 28. 2

111 26 22. 66 22. 4 25. 0 2 Breaking Strength (lbs/in.

width) Warp 26 26. 69 15. 40 35. 9 2 58. 4 29.0 76.0 F111 26 24. 30 13. 90 31. 1 2 43. 8 26. 0 55. 0

* Norm-Average based on tests of each sample.

A study of the above table shows that approximately a 100% increase in strength is realized when a chlorine containing atmosphere is utilized.

In light of the above findings, further experimental work was done to determine the elfect on final strength properties resulting from the use of chlorine containing atmosphere during the initial carbonization of the raw cellulosic material (room temperature to about 800 C.) as well as during the graphitization stage. Unfortunately, it was found that the use of a chlorine containing atmosphere in such a manner resulted in a destructive reaction which lowered the strength of the resulting product. However, subsequent testing uncovered the fact that if the chlorine containing atmosphere was present from room temperature to about 650 C. and then purged with nitrogen for the remainder of the 'bake to 800 C. a higher strength carbon product was attained. Bromine, iodine and fluorine containing atmospheres are likewise suitable for the room temperature to about 650 C. treatment. However, when a fluorine containing atmosphere is employed care must be taken to avoid the well known hazards associated with the use of fluorine in a hydrocarbon and/or hydrogen containing atmosphere, this being the atmosphere which results due to the hydrogen which is evolved fro-m the cellulosic material at such temperatures.

While the applicants do not wish to be bound to any theoretical limitations, it is believed that the above discussed phenomenon may be explained as follows:

Research in the study of cellulose pyrolysis has identified at least three typical steps in generation of elemental carbon from the carbohydrate cellulose structure. Dehydration of the molecule occurs above 200 C. and below 350 C. Decomposition of derived glucosans occurs between 350 C. and 650 C. Normal dehydrogenation occurs in a narrow temperature range between 650 C. and 800 C. The peak of the reaction is near 700 C. and the presence of chlorine is deleterious.

From the foregoing, it will be appreciated that the controlled use of a halogen and preferably a chlorine containing oxygen-free, non-carbonaceous purging atmosphere in the production of carbon and graphite fibrous textiles, i.e., from room temperature to about 650 C. and from 800 C. to until substantially complete graphitization has occurred gives a significant improvement in strength while an uncontrolled purge with a chlorine containing atmosphere throughout the entire process would have an adverse eifect on strength.

We claim:

1. A process for the production of flexible fibrous graphite from flexible cellulosic textile material which comprises carbonizing said cellulosic material in a baking oven, said baking oven being provided with an oxygenfree, non-carbonaceous gaseous atmosphere containing at least about 5% of a halogen gas while said temperature 7 is between approximately room temperature and 650 C.,

purging said atmosphere with a non-oxidizing, non-carbonaceous, halogen-free gas, and continuing carbonization to about 800 C., and subsequently graphitizing said carbonized material in an electric furnace while continuously sweeping the surface of said material with an oxygen-free, non-carbonaceous gaseous atmosphere contain ing at least about 5% of a halogen gas at temperatures from about 800 C. until substantially complete graphitization has occurred.

2. The process of claim 1 wherein said halogen gas is chlorine and said purging gas is nitrogen.

3. The process of claim 2 wherein said chlorine containing gaseous atmosphere comprises 20% chlorine and nitrogen.

4. In a process for the production of flexible fibrous carbon from flexible cellulosic textile material the improvement which comprises carbonizing said cellulosic material in a baking oven, said baking oven being provided with an oxygen-free, non-carbonaceous gaseous atmosphere containing at least about 5% of a halogen gas while said temperature is between approximately room temperature and 650 C., purging said atmosphere with a non-oxidizing, non-carbonaceous halogen free gas, and continuing ca-rbonization to about 800 C.

5. The process of claim 4 wherein said halogen gas is chlorine and said purging gas is nitrogen.

6. The process of claim 5 wherein said chlorine containing atmosphere comprises 20% chlorine and 80% nitrogen.

7. In a process for the production of flexible fibrous graphite from carbonized flexible cellulosic textile material the improvement which comprises graphitizing said carbonized material in an electric furnace while continuously sweeping the surface of said material with an oxygen-free non-carbonaceous gaseous atmosphere containing at least about 5% of a halogen gas at temperatures from above about 800 C. until substantially complete graphitization has occurred.

8. The process of claim 7 wherein said halogen gas is chlorine.

9. The process of claim 8 wherein said chlorine gas containing atmosphere comprises 20% chlorine and 80% nitrogen.

References Cited UNITED STATES PATENTS 3,011,981 12/1961 Soltes 252502 3,053,775 9/1962 Abbott 252421 3,107,152 10/1963 Ford et al 23209.2 3,116,975 1/1964 Cross et a1 23-2094 3,179,605 4/1965 Ohsol 252502 OSCAR R. VERTIZ, Primary Examiner.

EDWARD L. MEROS, Examiner, 

1. A PROCESS FOR THE PRODUCTION OF FLEXIBLE FIBROUS GRAPHITE FROM FLEXIBLE CELLULOSIC TEXTILE MATERIAL WHICH COMPRISES CARBONIZING SAID CELLULOSIC MATERIAL IN A BAKING OVEN, SAID BAKING OVEN BEING PROVIDED WITH AN OXYGENFREE, NON-CARBONACEOUS GASEOUS ATMOSPHERE CONTAINING AT LEAST ABOUT 5% OF A HALOGEN GAS WHILE SAID TEMPERATURE IS BETWEEN APPROXIMATELY ROOM TEMPERATURE AND 650*C., PURGING SAID ATMOSPHERE WITH A NON-OXIDIZING, NON-CARBONACEOUS, HALOGEN-FREE GAS, AND CONTINUING CARBONIZATION TO ABOUT 800*C., AND SUBSEQUENTLY GRAPHITIZING SAID CARBONIZED MATERIAL IN AN ELECTRIC FURNACE WHILE CONTINUOUSLY SWEEPING THE SURFACE OF SAID MATERIAL WITH AN OXYGEN-FREE, NON-CARBONACEOUS GASEOUS ATMOSPHERE CONTAINING AT LEAST ABOUT 5% OF A HALOGEN GAS AT TEMPERATURES FROM ABOUT 800*C. UNTIL SUBSTANTIALLY COMPLETE GRAPHITIZATION HAS OCCURRED. 